Microsoft’s Major Nelson posted an explanation of the problems I (and may other people) have been experiencing with XBox Live and our corrupt Gamertags.
I didn’t post about it when it happened, but MS finally contacted me back a week or so ago, and told me they couldn’t recover my gamertag. In compensation, they gave me 18 months of XBox Live to use. Not great, but at least I’ve got some closure and a few months of comped time. It doesn’t make up for the four years of fees I paid to keep my gamertag active, but its something.